1. Field of the Invention
The present invention relates to the field of fluidic processing, more particularly, to methods and apparatuses for a substantially contact-free manipulation of droplets in a fluidic processor.
2. Description of Related Art
A programmable fluidic processor (PFP) performs chemical and biochemical assays and synthesis. However, surface fouling and sample carryover are major issues in all biological assay systems because reaction mixtures may contain proteins, lipids, fatty acids and other molecules. Proteins generally have low hydration energies in their surface hydration shell making them easy to precipitate and to associate with surfaces. Similarly, fatty acids and lipids accumulate at hydrophobic-hydrophilic interfaces. Indeed, the interface between a polar and a non-polar medium develops a region of modified polarity in which bio-molecules may partition and exhibit accumulation, insolubility, and/or denaturation. Whenever a biological reagent-containing droplet wets a surface, it is almost inevitable that some degree of surface contamination can occur. Furthermore, electrical fields modify the association of amphiphilic materials at hydrophobic-hydrophilic interfaces. If the surface is the interface between the droplet and its suspending medium, rather than with a fixed surface, then that suspending medium may be replaced periodically to ensure that contamination is swept from the droplet processor and does not accumulate.
In the case of protein-containing droplets making contact with fixed surfaces, wetting by droplets as they move across the surface can produce a trail of denatured protein, resembling snails' tracks, and each passing droplet may add new protein or pick up some deposited by previous droplets. It is difficult to clean such proteins from surfaces and, obviously, contamination of the fixed reaction surface can render the droplet processor unusable at some point in time either through disruption of operation by carry-over interference or through modification of the surface wetting characteristics causing droplets to stick. This would seem to be a fundamental problem for droplet manipulation methods that rely on surface contact effects.
This shortcoming of conventional methodologies are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques concerning droplet manipulation in a fluidic processor; however, those mentioned here are sufficient to demonstrate that methodology appearing in the art have not been altogether satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.